2.2 Major Divisions of Spectral Wavelength Regions

The wavelength of electromagnetic energy has such a wide range that no instrument can measure it completely. Different devices, however, can measure most of the major spectral regions.

The division of the spectral wavelength is based on the devices which can be used to observe particular types of energy, such as thermal, shortwave infrared and microwave energy. In reality, there are no real abrupt changes on the magnitude of the spectral energy. The spectrum are conventionally divided into various parts as shown below:

The optical region covers 0.3 - 15 mm where energy can be collected through lenses. The reflective region, 0.4 - 3.0 mm, is a subdivision of the optical region. In this spectral region, we collect solar energy reflected by the earth surface. Another subdivision of the optical spectral region is the thermal spectral range which is between 3 mm to 15 mm, where energy comes primarily from surface emittance. Table 2.1 lists major uses of some spectral wavelength regions.

Table 2.1. Major uses of some spectral wavelength regions

Wavelength	Use	Wavelength	Use
g ray X ray Ultraviolet(UV) 0.4-0.45 µm 0.7-1.1 µm	Mineral Medical Detecting oil spill Water depth, turbidity Vegetation vigor	1.55-1.75 µm 2.04-2.34 µm 10.5-12.5 µm 3 cm - 15 cm 20 cm - 1 m	Water content in plant or soil Mineral, rock types Surface temperature Surface relief, soil moisture Canopy penetration, woody biomass